An optical fiber structure includes a first fiber array and a second fiber array, which are placed one on the other. For example, the first fiber array includes a substrate having four V-shaped grooves and four first optical fibers, the output ends of which are linearly arranged and fixed to the substrate, and the second fiber array includes a substrate having four V-shaped grooves and four second optical fibers, the output ends of which are linearly arranged and fixed to the substrate. The first optical fiber is a multimode fiber having a core and a cladding, and the core diameter is 60 μm and the outer diameter of the fiber is 80 μm. The second optical fiber is a multimode fiber having a core and a cladding, and the core diameter is 105 μm and the outer diameter of the fiber is 125 μm.